Powders of metal, silver and gold

ABSTRACT

A substantially homogeneous, finely divided powder, substantially free of silver chloride or cyanide comprising at least one metal other than silver or gold, and silver and gold, and an anti-agglomerating agent substantially homogeneously dispersed throughout said powder. The powders are particularly useful in the electronic arts.

United States Patent [191 Daiga Related [15. Application Data [62]Division of Ser. No. 141,006, May 6, 1971, Pat. No.

[52] US. Cl 75/.5 A [51] Int. Cl B22f 9/00 [58] Field of Search 75/.5 B,.5 A, .5 R, 165, 75/172, 173 R [56]- References Cited UNITED STATESPATENTS 3/1919 Fahrenwald 75/165 June 11, 1974 2,189,640 2/1940 Powell75/165 2,371,240 3/1945 Hensel et al. 75/173 R 3,141,761 7/1964 RBhm75/.5 B 3,345,158 10/1967 Block et a1 75/.5 A 3,427,153 2/1969Venkatesan et a1. 75/,5 A

Primary Examiner-W. W. Stallard Attorney, Agent, or FirmRichard B.Dence; E. J.

Holler 5 7] ABSTRACT A substantially homogeneous, finely divided powder,substantially free of silver chloride or cyanide comprising at least onemetal other than silver or gold, and silver and gold, and ananti-agglomerating agent substantially homogeneously dispersedthroughout said powder. The powders are particularly useful in theelectronic arts.

9 Claims, No Drawings made therefrom. More particularly, this inventionrelates to processes for making metal-silver-gold powders and thepowders resulting therefrom which are extremely homogeneous in natureand thus find .a wide variety of uses particularly in the electronicarts, such as those uses disclosed in concurrently filed, commonly ownedcopending application Ser. No. 140,988, filed May 6, 1971 in the name ofBernard Greenstein and entitled RESISTOR COMPOSITIONS AND METH- ODS.

a The value of metal oxides such as palladium oxide and the like aselectronically active materials has long been known. For example, as setforth in the abovecited commonly owned copending application, it. isknown, that in the microelectronic circuitry art, a resistive metal suchas palladium may be admixed with a glass binder and an organic vehicleto form a printing paste. The paste is then printed onto a dielectricsubstrate such as aluminum oxide or the like by the use of a screen ormask of the desired mesh and formed to provide the desired pattern. Thedesired pattem is then fired in air to oxidize the palladium topalladium oxide and form an electronically active device (e.g.resistor).

Unfortunately, many resistive metal oxides (including palladium oxide)have relatively large and negative temperature coefficients ofresistivity (hereinafter referred to as TCR) which must usually beadjusted if the resistor is to be operative for its intended purposes.In order to regulate this TCR, (and in effect to increase it to atolerable'level somewhere about i ppm/C) certain metals such as silveror gold have been alloyed with the resistive metal. In addition toregulating TCR, these additive metals have also been found to dilute thesystem and thereby control resistivity and increase the stability of theresistor.

The term stability is well-understood in the art and is used herein inaccordance with this well-known meaning. That is to say, stabilitydefines that characteristic of an electronic system which enables it tomaintain its resistivity value within tolerable limits over extendedperiods of time and use.

As further disclosed in the aforementioned copending application and asdisclosed in commonly owned, copending application Ser. No. 58,740 filedJuly 26, 1970, now U.S. Pat. No. 3,681,261 one of the major problemsattendant resistive metal systems 'is their great sensitivity to thefiring process used to formulate the ultimate device from its printingpaste. Slight fluctuations and/or variations in temperature during thefiring cycle, for example, greatly'change the resistivity of theresulting product. Air flow and firing times are further variables towhich the characteristics of the final product are extremely sensitive.Such sensitivity, of course, renders these oxide systems extremelydifficult to reproduce. Not only is reproducibility low, but for somereason, not entirely understood, stability is also very low.

While the additive metals used in admixture with the resistive metaloxide generally provide commercially tolerable stability to the system,they are generally found to detrimentally increase TCR, usually farabove the desirable i 0 ppm/C, when used in amounts sufficient to obtaintolerable stability. In this respect, and especially when silver is usedas the stabilizing metal, stability must be sacrificed for acceptableTCR; while, on the other hand, TCR must be sacrificed for acceptablestability. ln almost all instances, reproducibility,

..regardless of the metal stabilizers used, is detrimentall low.

The aforementioned commonly owned, copending application, Ser. No.58,740, filed July 27, 1970, discloses a unique and valuable solution tothe abovedescribed problems attendant these resistive metal oxidesystems, especially when these systems are used to form microelectronicresistors. The entire disclosure of this copending application isincorporated herein by reference.

In this copending application, the problems of stability, sensitivity,and reproducibility are eliminated by a unique process' which, wheneffected, produces extremely homogeneous alloys of palladium or otherresistive metals with at least one stabilizing metal. By achieving highhomogeneity, reproducibility is increased because sensitivity of thesystem to later processing such as firing and the. like is materiallydecreased. ln thisrespect, while one stabilizing metal alone can beemployed, it was found to be preferred to use at least two of thesemetals together in amounts which were found to syner'gistically reducetheir affect upon TCR. Thus, by using two metals in combination,excellent stability is attained without unduly increasing TCR. One ofthe most important of these combinations is a combination of silver andgold, usually in alloy form.

Generally speaking, this aforementioned copending application obtainedthe necessary degree of homogeneity for nonsensitivity of the palladium(or other resistive metal) with the stabilizing metal systems, byinitially forming an admixture of the resistive metals and stabilizermetals in the form of organometallic compounds and adding thereto ananti-agglomerating agent. Upon heating of the admixture of a sufficienttemperature and for a sufficient period of time, the org'anoconstituents are driven off and the admixture is concentrated to anextremely homogeneous powder. Such powders were found to be extremelyuseful when alloyed and employed with glass binders as resistorcompositions for microelectronic circuitry.

While the technique hereinabove described relative to this copendingapplication is extremely valuable, it has a few drawbacks attendant withit which make the finding of an alternative method of forming anextremely homogeneous powder of a resistive metal with a silver and goldsystem most desirable.' Examples of such drawbacks include therelatively high expense of the organometallic compounds used as startingmaterials and the pollution and danger caused by the volatilization-ofthe organo constituents during heating to powder form. It has also beenfound that many of the commercially available organometallics useful inthe practice of the invention'disclosed in the copending applicationcontain chlorine-bearing solvents. During the concentration step, thechloride ions have a tendency to react with the silver metal and therebyform silver chloride precipitate which contaminates the resultingpowder. As discussed more fully hereinafter, silver chloride cannot betolerated in any substantial amounts in resistor compositions.

It is a purpose of this invention to provide the art with an alternativeprocess for forming extremely homogeneous, finely divided powders ofresistive metals in combination with silver and gold, which process doesnot employ organometallic compounds and thereby overcomes theabove-described problems relative thereto. In this respect, it is afurther purpose of this invention to provide the art with a startingmaterial powder and a process for forming this starting material powderfrom which the unique resistors of the abovecited concurrently filedcopending application Ser. No. 140,988, filed May 6, 1971 in the name ofBernard Greenstein entitled RESISTOR COMPOSITIONS AND METHODS, canbeformed and the other teachinvention is to an extent greater than thatachievable by mere mechanical comminution or comminution and metalalloying. Thus, the term homogeneous is used herein to define adispersion of materials which goes beyond that achievable by thesemechanical or partially mechanical techniques.

As'exemplified by us. Pat. Nos. 3,390,98l and 3,385,799 and British Pat.No. l,004,652,"the basic concept of coprecipitating two electronicallyactive noble metals to thereby form a finely divided alloy of the twometals is known. 'Gnerally speaking, such a known process comprisesdissolving each of the metals in a common inorganic solvent such as, forexample, nitric acid, so as to form a solution of soluble salts (e.g.nitrates) of the two. metals. Thereafter, the solution is contacted witha reducing agent which simultaneously reduces the dissolved metalsaltsand precipitates them as pure metal alloy powders.

The prior art coprecipitationtechniques, as represented by the patentscited above, have several serious drawbacks. Firstly, they nevercontemplate the use of a system having more than two metals therein. Se-

condly, although they do make mention of theuse of silver and gold as acoprecipitate, the application of the disclosed techniques to theformation of such a coprecipitate has many problems and detrimentsattached ous and to be avoided. In summary, then, the art, by its priortechniques is unable to safely form a noncontaminated coprecipitate ofsilver and gold.

The problem of contamination of coprecipitated powders, particularly ofsilver and gold, is an especially acute problem in many arts such aswhere the powder is to be used, for example, in microelectronic devicessuch as conductors, resistors and the like. In microelectronicresistors, for example, substantially no contaminating silver chlorideor cyanide can be tolerated. Since, therefore, the prior artcoprecipitation techniques cannot provide a safely formed,noncontaminated powder comprised of silver and gold, they are incapableof satisfying a specific but important need in the art. Therefore, inaddition to the above-explained need relative to anew technique forforming homoge neous, finelydivided powders which do not employorganometallic compounds, there also exists adefinite need in the artfor a new technique for forming homogeneous, finely divided metalpowders which include both silver and gold in their composition makeup,whichis safe'to conduct and which eliminates or substantially reducesthe contamination problem.

It is the purpose of this invention not only to. fulfill the firstabove-described need, but also to fulfill this latter need relative to anew technique wherein silver and gold may both be present in the powdercomposition but without the degree of metal salt contaminationexperienced when employing the prior art techniques.

In fulfilling the above-described needs, this invention generallyenvisions two alternative techniques for forming homogeneous, finelydivided powders of one or more metals in combination with silver andgold (or two other metals which give rise to similar problems ofcontaminated coprecipitation as silver and gold).

The first alternative technique of this invention generally comprisesforming a soluble salt solution of a thereto. For example, there areoniy 'a very limited number of inorganic media in which both silver andgold are soluble. Of these, aqua regia (e.g. 3 parts HCl to 1 part HNO3)and the various inorganic cyanide solutions are, generally speaking, theonlyones which feasibly could be employed. While aqua regia maygenerally be safely employed, insoluble silver chloride is formedsimultaneously with the silver and gold soluble salts, thus forming acontaminant in the ultimately precipitated metal alloy powder. Silvercyanide is somewhat more soluble than silver chloride. However, cyanidesalt contamination often does occur to a limited extent and may become amaterial problem especially when a high degree of silver isv required tobe present in the system In addition, the use of cyanides is dangermetalother'than silver or gold, and silver and thereafter reducing thesolution in accordance'with prior, art techniques similar to thosedescribed in the aforementioned patents. Such a reduction reaction withagitation forms a metal-silver slurry. To this metal-silver slurry isthen added gold inthe form of agold salt solution generally of thechloride type. The slurry solution now containing gold is then contactedwith a reducing agent either already present or additionally added, toprecipitate the gold into the metal-silver slurry and thereby form thetrimembered powder of metal, silver and gold.

cepts were carried out by dissolving gold, silver andmetal in, forexample, an aqua regia medium which would serve as a medium for allthree of these metals. This is because the initial reduction of themetal and silver into a powdered slurry renders the metal and silverless sensitive to chlorination.

The second alternative method contemplated by this invention providesfor the total elimination of the formation of any insoluble silverchloride or cyanide in the system andjthus is preferred wherenoncontaminated powders are required to be used such as in themicroelectronics art, particularly for making resistors and the like.This second alternative method generally comprises initially forming asoluble salt solution of the metal or metals other than silver or gold,and silver in a manner similar to the first alternative method. To thissilver-metal salt solution-there is then added a finely divided goldpowder usually having a particle size less than about 5 microns,preferably less than about 2 microns, and most preferably substantiallysubmicron in size. The solution containing the gold powder, which is notsoluble in the salt solution, is then thoroughly mixed as by agitation,to form a slurry of the gold and there is then added thereto a reducingagent for the metal and silver. While some small amount of homogeneityis sacrificed because the gold powder is not precipitated, precipitationof the metal and silver into the slurried gold powder effects asubstantial amount of homogeneity to the extent that excellent productscan be made therefrom for the purposes of microelectronic circuitry,particularly in the resistor area.

In view of this second alternative technique, this invention for thefirst time provides the art with a unique powder also considered a partof this invention. Such a powder generally comprises a substantiallyhomogeneous admixture of at least one metal other than silver or gold,with silver and gold, which admixture is substantially free of silverchloride or cyanide. As stated above, the homogeneity achieved andcontemplated is beyond that achievable by known mechanical comminutionand/or alloying techniques and is usually to the point where the silverand other metal are actually alloyed together according to X-raydiffraction indications with the gold highly dispersed therethroughout.The particle size of the powder, without comminution is generally lessthan about 5 microns and usually submicron in size and thus the powderis said to be finely divided."

Regardless of which of the above two alternative methods is employed tomake the finely divided homogeneous powders of this invention, thisinvention relates generally to all systems wherein at least one finelydivided metallic powder other than silver and gold must be formulated inadmixture with both silver and gold. In this respect silver and goldwill be referred to hereinafter since they are the preferred combinationwith which this invention deals. However, it is understood, as stated,above that this invention, as an equivalent, contemplates other metalcombinations which experience the difficulty of contamination bycoprecipitation similar to that of silver and gold.

The metal used in admixture with the silver and gold must be capable offorming a soluble salt in a liquid reaction medium in which a silversalt is also soluble. In addition, the soluble salt of the metal as wellas that of the silver must be capable of being coprecipitated inmetallic form by the addition of an appropriate reducing agent thereto.

The preferred metals for the purposes of this invention are the knownresistive metals such as, for example, palladium, rhodium, iridium,ruthenium, indium, and mixtures thereof. Of these, palladium is the mostpreferred for the preferred environmental use of microelectronicresistors because of its excellent resistive properties. Examplesofother metals useful in combination with silver and gold includeplatinum, copper, nickel, and mixtures thereof. i

The metal'or metals employed may be formed into any of their known saltswhich are soluble in a liquid medium in which a silver salt is alsosoluble. Therefore,

the formation of the metal salt and silver salt may be independent orsimultaneous. In addition, the metal and silver anion may be the same ordifferent, the only criteria being that both salts are soluble in acommon liquid medium and capable of being precipitated in metallic formfrom the medium by the addition of a reducing agent thereto, preferablywithout the formation of any insoluble salt occurring which cannoteasily be removed from the powdered solution. I

In the preferred embodiments of this invention, the liquid reactionmedium employed is water; In still more preferred embodiments, at leastone of the metals is palladium, and the soluble salts formed are, atleast in part, the soluble nitrates of palladium and silver. Nitratesalts, of palladium and silver are simply formed by reacting the silverand palladium with nitric acid. In this respect, and because of theready commercial availability of silver nitrate solutions, it ispreferred to form the metal-silver nitrate salt solutions of thisinvention by separately forming a nitrate solution of the metal andthereafter add a commercially prepared silver nitrate solution thereto.1

Examples of anions other than the nitrates which may be employedto form,in a known way, the soluble salts of one or more of the metals and/or ofthe silver include: sulfates, sulfites, bromates, chlorites, fluorides,permanganates, nitrites, and the like.

Salts formed of the nitrate anion are generally soluble in water of roomtemperature or below as are some of the salts of the other exemplaryanions listedabove. In other instances, the anion salt may be of limitedsolubility and thus the liquid medium may have to be heated or cooled inorder to form and/or maintain a truly soluble solution prior to andduring formation of the powders according to this invention ifcontamination with the anion or salt thereof is to be avoided orlimited.

, The reducing agents which cause the precipitation of metal and silverfrom their medium may be any of the well-known reducing agents orcombinations thereof commonly employed in. the art. Examples of suchreducing agents include hypophosphorous acid (HgPOg), a mixture ofsodium formate and sodium borohydride, a mixture of hydroxylamine andsodium borohydride, a mixture of formic acid and hypophosphorous acid, amixture or hydrazine sulfate and hypophosphorous acid, a mixture offormic acid and hydroquinone or a mixture of tartaric acid andhydroquinone, or sodium bisulfite. H PO is preferred especially withsilver and palladium since minimal side reactions and substantially noinsoluble contaminating salts are formed when it is used.

The reducing agents addedto effect gold precipitation in the firstalternative technique may be any of the well-known reducing agents forgold such as sodium sulfite, hydroquinone, hydrazine sulfate, sulfurousacid, zinc dust, ferrous sulfate, and the like. Sodium sulfate I ispreferred because it is readily available and causes the formation of anexcellent particle of gold upon its precipitation.

In order to insure homogeneity and obtain powders in their best possibleform, especially for use in the microelectronic circuitry art, ananti-agglomerating agent is preferably added to the salt solution priorto any coprecipitation so as to be a part of the ultimately formed,

homogeneous, finely divided powder, regardless of the alternativetechnique employed. Such antiagglomerating agents are inert to thesystem and form I 7 a slurry-therein. The anti-agglomerating agentsusually employed are, of a fine particle size, i.e., less than aboutmicrons and usually submicron in size. Examples of these agents includeultra-fine alumina, an ultra-fine TiO and other ultra-fine refractories.Preferred for the purposes of this invention is ultra-fine silica(submicron in size) which is purchasable under the trademark CAB-O-SIL.

The percentages of the various ingredients employed will vary over awide range depending upon the ultimate use to which the powder may beput. it is an aspect of this invention that the percentages attainableare quite flexible in nature. Thus, for example, homogeneous, finelydivided powders are attainable which contain less-than 1% of any givenmetal and more than 99% of another metal. In the preferred uses, asdisclosed inthe aforementioned copending Greenstein application, themetal other than silver and gold is a resistive metal such as palladiumor the like which may constitute from about 5-95% by weight of thepowder. Preferably the resistive metal constitutes l5-75% by weight ofthe powder, and most preferably -65% by weight thereof.

In preferred embodiments-the remainder, i.e. 95-5% by weight, of themetal content is a combination of silver and gold in a weight ratio of4:1 to 1:4 with respect to each other. in those instances where anantiagglomerating agent is employed, such usually need only be employedin amounts of about 0.5-l5% by weight of the total powder, preferably 2l 0% by weight herein by reference.

and as where ultra-fine silica is employed, usually about 5% by' weight.

The concentrations employed for making the soluble salt solutions of themetal, silver and gold, and the amount of gold powder employed in' thesecond alternative technique are matters generally of convenience andmayvarywidely in order .to insure the requisite amounts of the variousingredients in the final powder and at the same time be workable in themanufacturing system devisedJGenerally speaking, the upper limit ofconcentration is the saturation point of the solution for the salt whilethe lower limit is a practical volume consideration. In this respect,concentrations of the salt solutions lower than about 10% are normallynot employed. In the preferred instances where palladium and silver arefirst formed into a soluble nitrate solution by reaction with nitricacid, the solution containing the two salts may have a concentration onthe order of about 2060% of the combined salts. Similar concentrationsfor the gold solutions in the first alternative technique may also beemployed. The relative concentrations of each metal within thesesolutions are then,

of course, adjusted in a known manner to achieve the desired powder uponreduction and precipitation.

The gold solutions employed in the first alternative technique may beany'well-known soluble-salt solution of gold. Generally speaking, suchsoluble salt solutions include the various chloride and cyanide salts ofgold.

' A particularly preferred gold solution for the purposes of thisinvention is a solution of 'hydrochloroauric acid formed in aconventional manner by dissolving the'requisite amount of gold inaqua-regia (eQg. 3-4 parts HCl to 1 part HNO The gold powder employed inthe second alternative technique may be any commercially available goldpowder preferably having a particle size of less than about 5 microns. Apreferred gold powder, because of I Generally speaking, this copendingapplication discloses a method for forming a gold powder, usually havinga bulk density greater than about 5.0 grns./cc and a particle size oflessthan about 5 microns, which comprises initially dissolving agold-bearing material in a HCl-HNO acid. Thereafter, there is added tothe solution an effective amount of an emulsifying agent capable ofcoating freshly formed gold particles and preventing coalescence andcold-welding thereof and keeping the particle size of said goldparticlesless than about 5 microns. To this solution there is then addeda precipitating agent, which precipitates gold powder from solutionsubstantially free of contaminating chloride or other salts. Theso-formed gold particles are encapsulated with the emulsifier which isremoved, usually by washing the powder in a solvent such as acetone orwater and then drying the powder prior to using it in this invention.The powder so formed is substantially pure, uncontaminated, gold powderof the indicated particle size.

A typical operating procedure for conducting the first alternativetechnique described hereinabove is to initially prepare a metal-soluble,salt solution by dissolving the metal in aninorganic acid. For example,palladium in commercial sponge, powder or other form may be dissolvedina 70% solution of l-lNO to form a solutionpreferably of about 300-400gms/l. of Pd. A separate silver nitrate solution may be prepared withnitric acid or commercially obtained. Alternatively, silver sponge,powder, etc. may be added with the palladium in the requisite amounts tothe 70% HNO solution. The gold solution is prepared by dissolving a goldsponge, powder, etc. in aqua regia and removing excess l-lNO by heatingthe solution. A typical concen- The nitrate solutions of silver andmetal (e.g. palladium) are then admixed if not simultaneously formed andan antiagglomerating agent is added thereto. The solution is agitated toslurry the antiagglomerating agent and a reducing agent such as H PO orsodium bisulfite is added to precipitate the metal and silver in theirmetallic form. Generally speaking, it is desirable to precipitatesubstantially all metal and silver from the solution, the ratio of metalto silver being controlled by the concentrations and amounts ofsolutions formed. For this reason, at least a stoichiometric amount ofreducing agent and preferably about 2 or 3 times in excess of thisamount, is employed to insure substantially dium. To this slurriedsolution is then added the hydrochloroauric acid solution. In thoseinstances where the reducing agent initially employed for the metal andsilver is also a reducing agent for gold, gold precipitate will formupon mere addition of the gold solution to the s 9 slurry. In such anevent, sufficient reducing agent is added initially to insure thatsubstantially all of the gold is precipitated from solution. in thoseinstances where a different reducing agent is employed .or the reducingagent initially added is insufficient to precipitate gold, a reducingagent is added with continued vigorous agitation until the precipitationof the gold is substantially complete. The reduction reaction of golddoes result in some reaction occurring between the slurried silver andthe chloride ions in the decomposed hydrochloroauric acid. However, asstated above, because the silver is previously precipitated, a reductionin the amount of insoluble AgCl normally formed by commoncoprecipitationof gold and silver from a common aqua-regia solution is obtained.

The homogeneously dispersed finely divided powder of metal, silver,gold, anti-agglomerating agent, and reduced amounts of AgCl is nowseparated, as by filtration, from the liquid medium and dried. Aspreviously stated, the powder is of particles less than about micronsand usually less than about 1 micron. in addition, the homogeneity ofdispersion of the individual ingredients is far beyond thatachievable bysimple comminution and/or alloying. Furthermore, it has been found thatin most instances, as indicated by X-ray defraction techniques, thesilver is alloyed with the metal.

. In a typical procedure for conducting the second alternative techniquedescribed hereinabove the solutions of metal and silver, preferably innitrate form, are formed and admixed in a manner similarly as describedin the first alternative technique. Gold powder having a particle sizeof less than about 5 microns is then added to the common solution.Preferably, as stated, the gold powder is that as produced by myafore-cited copending application. The anti-agglomerating agent is addedeither prior to, simultaneously with, or after the gold powder is addedand the particles of this agent and gold are slurried in the solutionwith vigorous agitation.

A reducing agent in the before-described amounts is then added toprecipitate the metal and silver and the homogeneous powder is obtainedand processed similarly as described with respect to the firstalternative technique. The product of the second alternative tech-EXAMPLE 1 FIRST ALTERNATIVE TECHNIQUE A gold reactant solution (l-iAuCh)was prepared from' pure gold sponge. This was accomplished by reacting20 gms. of Au in an aqua-regia solution and diluting the solution to T60ml. with H O. A palladium nitrate solution was prepared by dissolving53.8 grams of the metal in 150 ml (70%) HNO The resultant Pd (NOsolution had a volume of 160 ml. A silver nitrate solution wasformed bydissolving 1 15.3 grams of silver nitrate crystals in 150 ml. ofdistilled water. The total volume of the resultant solution was 175 ml.

To start the process 80 ml. of the Pd (N09 solution,

87 ml. of the AgNO solution, and 100 ml. of H 0 were tinued agitationthe reduction reaction was carried out by adding 170 ml. of a solutioncontaining grams of NaHSQ, to the reactor. The Nal-lSO addition tookplace over a 14 minute time interval and the reaction media wasmaintained at 38 C.

Agitation was continued to slurry the precipitated silver and palladiummetals with the anti-agglomerant and the slurry was prepared forl-lAuCl, addition and reduction by the addition thereto of 15 grams ofNa SO in 100 ml. of H 0. This was followed by rapid addition of ml. ofthe l-lAuCl, solution. An additional ml. of the Na SO solution was addedto insure complete reduction of the gold. After 5 minutesof furthermixing, the agitator was shut off.

. After permitting the reactants to settle out for 30 minutes, thesolids were separated from the liquid by filtration. The solids werewashed by slurrying in l-l O and filtering several times. The final washwas followed by drying at C overnight. A finely divided,homogeneouspowder was obtained. The powder analyzed as containing on ametal basis by weight, 47.4% Ag, 14.55% Au, and 38.05% Pd. The powderalso contained 13.02% by weight chloride salt, assuming all chlorides tobe silver chloride.

EXAMPLE 2 a SECOND ALTERNATIVE TECHNIQUE 250 gms. of a powder consistingof by weight 52% Ag, 35% Pd, and 13% Au'were prepared by the followingtechnique.

A Pd(l\l0 solution was prepared by adding 87.5

grams of palladium metal to 245 ml. of a 70% HNO,

solution. The addition-of Pd to the acid was conducted slowly and thenitrous oxide gas formed was vented. An AgNO solution was prepared byadding 204.3 grams of AgNO crystals to 500 ml. of distilled water withstirring. The gold powder employed had a particle size of less than 5microns and was produced in accordance with Example 1 of myaforementioned copending application. 32.5 grams of the powder werewashed free of emulsifier in acetone and thoroughly-dried for usehereinafter.

The AgNO solution was charged into a reaction vessel which consisted ofa 5 liter glass baffled flask with a propeller type agitator. Thereaction vessel was provided with a heating and cooling bath to regulatethe temperature. One liter of distilled water was added and the solutionmixed rapidly by the propeller agitator. At this time, 12.5 gms. ofCAB-O-SIL (ultrafine SiO anti-agglomerating agent was suspended in thereaction medium. Five minutes of vigorous stirring were then allowed toproceed.

Next, the Pd(NO3)2 solution was added and the 32.5 gms. of gold powdersuspended in the combined solution with continuing agitation. Anadditional 375 ml. of distilled water were also added to aid in thewashing in of the gold powder.

The reduction reaction was initiated, with continued vigorous agitation,by adding to the reaction mass, dropwise, 390 gms. of a 50%hypophosphorous acid solution diluted in 400 ml. of distilled water. Thetotal time to add all of the H PO was about hour. During that time theresulting exothermic reaction was maintained at about 50 C by coolingwater. After the reducing agent had been added the reaction media washeld at the reaction temperature with mixing for l hour'to insurecompleteness and optimum homogeneity of the metal slurry.

Thereafter, the metal slurry was filtered and washed with about twoliters of distilled water and placed in a 1 C drying oven overnight.

The resulting dry powder was a microscopically homogeneous black masshaving substantially no particles greater than about 5 microns. Analysisindicated the powder to consist on. a metal basis of, by weight, 52% Ag,35% Pd, and 13% Au and further indicated that no contaminating saltswere present therein. This powder, as evidenced by the examples in theaforementioned copending-Greenstein application, may be used as avaluable starting material for microelectronic resistor production.

Once given the above disclosure many other features, modifications,andimprovements will become apparent to theskilled artisan. Such otherfeatures, modifications, and improvements are therefore considered to bea part of this invention, the scope of which is to be de terminedby thefollowing claims.

I claim: t v

l. A substantially homogeneous, finely divided powder, substantiallyfree of silver chloride or cyanaide comprising at least one metal otherthan silver or gold, and silver and gold, and an anti-agglomeratingagent substantially homogeneously dispersed throughout said powder. I

2. A powder according to claim 1 wherein said powder has a particle sizeless than about 5 microns.

3. A powder according to claim 1 wherein said at least one metal isselected from palladium, rhodium, iridium, ruthenium, indium,and'mixtures thereof.

4. A powder according to claim 1 wherein said at least one metal is thesingle metal palladium.

5. A powder according to claim 1 wherein said antiagglomerating agent isparticulate silica submicron in size.

6. A powder according to claim 1 consisting essentially of about: 595%by weight palladium, 5-95% by weight of an admixture of gold and silverin a weight ratio of about 4:1 1:4, and about 0.5-1 5% by weightanti-agglomerating agentf 7. A powder according to claim 1 whichconsists of about 20-65% by weight palladium, about -35% by weight ofsaid silver, gold admixture, and about 5% of submicron particle sizesilica'as said anti-tagglomerating agent.

8. A powder according to claim 1 consisting of by weight about: 52% Ag,35% Pd, and 13% Au on a metal basis, the total composition includingabout 5% by weight of said silica.

9. A powder according to claim 1 wherein said palladium is indicated asalloyed with said silver by X-ray diffraction techniques.

2. A powder according to claim 1 wherein said powder has a particle sizeless than about 5 microns.
 3. A powder according to claim 1 wherein saidat least one metal is selected from palladium, rhodium, iridium,ruthenium, indium, and mixtures thereof.
 4. A powder according to claim1 wherein said at least one metal is the single metal palladium.
 5. Apowder according to claim 1 wherein said anti-agglomerating agent isparticulate silica submicron in size.
 6. A powder according to claim 1consisting essentially of about: 5-95% by weight palladium, 5-95% byweight of an admixture of gold and silver in a weight ratio of about4:1 - 1:4, and about 0.5-15% by weight anti-agglomerating agent.
 7. Apowder according to claim 1 which consists of about 20-65% by weightpalladium, about 80-35% by weight of said silver, gold admixture, andabout 5% of submicron particle size silica as said anti-agglomeratingagent.
 8. A powder according to claim 1 consisting of by weight about:52% Ag, 35% Pd, and 13% Au on a metal basis, the total compositionincluding about 5% by weight of said silica.
 9. A powder according toclaim 1 wherein said palladium is indicated as alloyed with said silverby X-ray diffraction techniques.